Nocturnal Dynamics of Sleep-Wake Transitions in Patients With Narcolepsy

Introduction: We investigate how characteristics of sleep-wake dynamics in humans are modified by narcolepsy, a clinical condition that is supposed to destabilize sleep-wake regulation. Subjects with and without cataplexy are considered separately. Differences in sleep scoring habits as a possible confounder have been examined. Aims and Methods: Four groups of subjects are considered: narcolepsy patients from China with (n = 88) and without (n = 15) cataplexy, healthy controls from China (n = 110) and from Europe (n = 187, 2 nights each). After sleep-stage scoring and calculation of sleep characteristic parameters, the distributions of wake-episode durations and sleep-episode durations are determined for each group and fitted by power laws (exponent a) and by exponentials (decay time tau). Results: We find that wake duration distributions are consistent with power laws for healthy subjects (China: alpha = 0.88, Europe: alpha = 1.02). Wake durations in all groups of narcolepsy patients, however, follow the exponential law (tau = 6.2-8.1 min). All sleep duration distributions are best fitted by exponentials on long time scales (tau = 34-82 min). Conclusions: We conclude that narcolepsy mainly alters the control of wake-episode durations but not sleep-episode durations, irrespective of cataplexy. Observed distributions of shortest wake and sleep durations suggest that differences in scoring habits regarding the scoring of short-term sleep stages may notably influence the fitting parameters but do not affect the main conclusion.